As we explained in our original article, the vulnerability was only exploitable through certain routes, and we disclosed the problem to EE ahead of publication. Last night, the network gave us this statement:

Thanks to Simon and The Register for bringing this to our attention. Our engineers have worked hard since then to identify the root fault and work on a fix. We can now confirm that we have urgently updated our systems and patched the issues raised in the article.

The Register plans to test the fix over the next few days. In particular we suspect that what left the door open was a combination of the merger of the Orange and T-Mobile UK brands – where signalling information was not exchanged between the systems – and a model that allows customers who are roaming to pick up their voicemail without having to enter a PIN.

Of course there is a balance between ease of use and security. We must admit, it is handy that you don’t have to enter a PIN every time you want to pick up your voicemail from your mobe, and you don’t really want to have to enter a PIN just because you are roaming. But if the cost of this ease of use is general security, it is certainly an issue that needs to be addressed.

We hope to have a meeting with EE’s voicemail engineers to talk through the finer details of the exploits.

In the meantime we recommend customers on Three – also affected by the voicemail spoofing bug – heed the network's advice and set a mandatory login PIN for their inboxes. ®